A klystron is a device that converts the kinetic energy of a direct current (DC) electron beam into radiofrequency (RF) energy. Klystrons have been used in a variety of applications. For example, klystron may be used to provide RF energy to a particle accelerator, such as an electron accelerator, to cause the accelerator to generate a particle beam with a certain desired characteristic. In some cases, the particle beam may be used to produce a radiation beam for treatment or diagnostic purpose. Klystrons may also be used to produce reference signals for superheterodyne radar receivers, and high-power carrier waves for communications.
A klystron may include an electron gun, two or more resonant cavities through which the electron beam propagates, and a collector which captures the spent electron beam and dissipates the resultant heat. The simplest klystron has two cavities—an input cavity and an output cavity. In the input cavity, microwave energy excites the cavity resonance. The resultant electric field that is produced in the beam tunnel modulates the DC electron beam. In one half period of the RF wave, the electrons lose energy from the electric field in the resonator and decrease velocity. In the next half period, the electrons gain energy and increase in velocity. The change in velocity is small but the sinusoidal variation in beam velocity causes the electrons to bunch together and produce a sinusoidally varying RF beam current.
The output cavity of the klystron may be situated at the position along the beam path where the RF current has reached a desired value, e.g., a maximum value. As the electron bunches pass through the output cavity, they induce currents on the surface of the cavity walls, which in turn produce a resonant mode in the output cavity. The resonant mode produces an electric field that decelerates the electron bunches and converts the electron beam kinetic energy into RF energy. The RF energy is then coupled out from an output cavity at the resonator. In some cases, additional resonant cavities may be placed between the input and output cavity to increase the gain of the klystron, or to modify the frequency response and bandwidth of the device.
Existing klystrons produce a cylindrical electron beam with a circular cross section that propagates down a cylindrical beam tunnel and interacts with resonant cavities that are figures of revolution. However, Applicants determine that it may be desirable to have klystrons that produce an electron beam with an elongate cross section. In addition, Applicants determine that it may be desirable to provide more than one output cavities at the klystron that are uncoupled from each other.